Thermal overload switch



April 21, 1953 H. L. BRUMP THERMAL OVERLOAD'SWITCH Filed Feb. 9, 1951 INVENTOR. HERBERT L. OBZUMP. BY 4.

Patented Apr. 21, 1953 THERMAL OVERLOAD SWITCH Herbert L. Bruinp, Dayton, Ohio, assignor, by mesne assignments, to Etc Inc., Niles, Mich.

Application February 9, 1951, Serial No. 210,180

Claims.

This invention relates to a switch and more particularly to a thermal overload switch.

The Underwriters Laboratories set forth definite standards which must be met by 9, switch in order to obtain their approval. These standards are difficult to meet in that the switch must consider both the degree of overload and the duration of the overload.

It is an object of this invention to provide a low cost thermal overload protector switch wherein a relatively small momentary overload will not open the circuit but a relatively large momentary overload or a smaller prolonged overload will open the circuit.

More particularly, it is an object of this invention to provide a simple switching arrangement wherein the temperature responsive element is partially protected against direct radia tion from the heater which operates the switch, so that the switch will not respond too rapidly to an overload unless the overload exceeds a pre determined value.

Still another object of this invention is to provide an improved switch wherein the thermal responsive snap mechanism constitutes a subassembly which is adjustably mounted on a base.

Still another object of this invention is to provide a thermal overload switch in which the heating element may be readily removed and replaced without disturbing the rest of the switch mechanism.

Another object of this invention is to provide a simplified arrangement for making electrical contact with the switch subassembly.

Other objects and advantages reside in the construction of parts, the combination thereof and the mode of operation, as will become more apparent from the following description.

In the drawing:

Figure 1 is a side elevational view of a preferred embodiment of my invention;

Figure 2 is a sectional view taken substantially on line 2-2 of Figure 1;

Figure 3 is a sectional view taken substantially on line 33 of Figure l; and

Figure 4 is an exploded perspective view showing the relationship of the various parts.

Referring now to the drawing wherein I have shown a preferred embodiment of my invention,

reference numeral ill designates an insulating base which serves to support a pair of stamped sheet metal terminal elements l2 and I4. These terminal elements are held in place on the base by means of screws l6. As best shown in Figure 4, each of the terminal elements is provided with a tapped opening la. The tapped openings l8 cooperate with the screws 20 to hold a heating element 22 in place. When the terminals l2 and it are connected into an electric circuit, the current flowing in the circuit is thus required to pass through the heating element 22 for a purpose to be explained more fully hereinafter.

The circuit making and breaking device which is adapted to respond to excessive heating caused by the flow of an abnormally high current through the heating element 22 consists of a subassembly generally designated by the reference numeral 24. The subassembly consists of a knurled mounting stud 26 which projects into a hole 28 formed in the base for the purpose of snugly receiving the stud 26. The 'subassembly includes a spring conductor element 30 which is adapted to press against the bottom wall 32 of the insulating base i 0, as best shown in Figure 2. so as to urge the mounting stud 26 outwardly in a direction away from the bottom wall 32. The one end of the spring element 30 is adapted to press against a resilient U-shaped terminal or contact element 34 which is adapted to be held in place between the spring element 30 and the bottom wall of the recess in the base, as best shown in Figure 2. A lead wire 36, which has its one end projecting through the side wall of the base ID, is soldered to the contact element 34 as shown and this lead wire helps to hold the contact element 34 in place before the subassembly is mounted in place. The other end of the spring element 30 is provided with a flange in the form of spaced feet that extend away from the base ID.

A bimetallic snap spring element is anchored at its midpoint to the stud 26 as shown. A movable contact 42 is secured to the one end of the element 4!] and cooperates with a stationary contact 44 secured directly to the terminal l2 to serve as a stop for the said one end of the element 40. The bimetallic element is a conventional one piece element having longitudinally extending slots 46 provided as shown, so as to form three parallel strips connected at their ends. The two side strips are crimped as at 45 whereby they are in effect shorter than the central strip and this then forms a conventional over center snap switch of the type in which heating of the bimetallic material serves to cause actuation of the movable contact carried at one end of the bimetallic element. Bimetallic snap elements of this general type are well known and need no further explanation.

Upon becoming heated, the bimetallic element will move its full line position as shown in Figure 2 to its dotted line position. In the dotted line position one end of the bimetallic element is engaged by the flange end of the spring element 38 and is thus limited in its movement beyond the over-center position. Thus the metallic element is reset more easily by a reset button that will be described presently. The heat for actuating the bimetallic element is produced by the heating element 22.

A shield 50 is provided between the heating element 22 and the bimetallic element G so as to prevent momentary insignificant overloads from causing the circuit to open. However, this shield does not prevent prolonged overloads of a predetermined value from causing operation of the switch. The shield 50 is preferably, though not necessarily, made in the form of a copper stamping and constitutes a part of the subassembly in that it is attached directly to the end of the stud 26. The shield is mounted on the stud by means of its central portion, which is pressed out of the plane of the shield so that the shield contacts the bimetallic element only over a limited area at the stud. Thus the efiiciency of the shield is high.

In order to reset the switch after an overload, there is provided a reset button 52 which is supported in the base Ill, as best shown in Figure 2. This reset button is provided with a flange 5 3 which is adapted to engage that end of the bimetallic element 40 which is opposite the end engageable by the flanged end of the spring element 30 when it is desired to reset the bimetallic element. A coil spring 56 biases the reset button outwardly, as best shown in Figure 2.

An insulating insert 58 serves as a stop for the one end of the bimetallic element 46 and thereby serves to insulate the'bimetallic element from the terminal M.

The temperature at which the bimetallic element E9 is adapted to open the circuit is determined by the nearness to over-center position of the bimetallic element 42 when engaging the electrical contact 44 and the insulating contact 58 as shown in full lines in Figure 2. Such nearness to over-center is determined by the position i of the said region of the bimetallic element on the stud with respect to the contacts 44 and 58 and this position is in turn determined by the location of the mounting stud 26 within the recess 28. Thus, in the manufacture of the switch, the mounting stud is accurately positioned, and once it is properly positioned, it is held in place by the set screw 60 (see Figure 3). Before the switch leaves the factory, an insulating plug 62 is inserted into the aperture 28. Likewise, a sealing plug '64 protects the set screw 68, as best shown in Figure 3. The spring element 30 and the resilient contact 34, by virtue of their spring construction, will engage one another in any position of the stud 26 within the recess 28.

Thermal overload switches of the type shown herein are usually, though not necessarily always, used in motor control systems. The heater 22 is adapted to be connected directly in the motor circuit and the switch contacts 42 and 44, the bimetallic element 42, the spring element 30, the resilient terminal 34, and the lead wire 36 are adapted to be connected in circuit with a magnetic type of motor control switch (not shown) so that when the contacts 42 and 44 separate in response to a thermal overload caused by the excessive flow of current through the heater 22, the magnetic motor control switch will open the main motor circuit; The reset button 52 must be pressed in order to reset the bimetallic element ill so as to reclose the motor control circuit.

It is to be noted that the heating element 22 is secured to the sides of the terminals l2 and M opposite the sides at which the bimetallic element 42 is positioned for engagement with the fixed electrical contact 44 and the insulating insert or contact 58 mounted respectively on the terminals [2 and I4, and that the portion of the mounting stud 26 in the recess 28 in the insulating base l0 lies on the side of the bimetallic element 42 away from the heating element 22. Thus the heating element 22 may be removed and replaced without interference with the bimetallic element 42 or the other part of the subassembly.

Although the preferred embodiment of the devise has been described, it will be understood that within the purview of this invention various changes may be made in the form, details, proportion and arrangement of parts, the combination thereof and mode of operation, which generally stated consist in a device capable of carrying out the objects set forth, as disclosed and defined in the appended claims.

Having thus described my invention, I claim:

1. A thermal overload switch comprising; a molded insulating base; first, second, and third terminals carried by said base; a heating element connected across the first and second terminals; circuit making and breaking mechanism comprising a subassembly; and means for adjustably supporting said subassembly on said base; said subassembly comprising a mounting stud, a bimetallic snap element carried by said stud and arranged in spaced relationship to said heating element so as when heated to snap out of electrical connection with the first terminal, a spring conductor carried by said stud and having one end arranged to press against the third terminal so as to cooperate with the snap element in electrioally connecting the first and third terminals, and a shield supported by said stud between said bimetallic element and said heating element so as to provide at least partial protection of the bimetallic snap element from direct radiation from said heating element.

2. A thermal overload switch comprising a molded insulating base having a recess formed in the one face thereof; a resilient contact disposed within said recess; a fixed contact carried by said base; a heating element supported on said base over said recess; circuit making and breaking mechanism supported in said recess; and means for adjust-ably supporting said mechanism relative to said heating element; said mechanism comprising a subassembly having a bimetallic element arranged in spaced heat exchange relationship to said heating element, a movable contact carried by said bimetallic element for engaging said fixed contact, a shield supported between said bimetallic element and said heating element so as to at least partially protect the bimetallic element against direct radiation from said heating element, and a spring conductor having one end arranged to press against said resilient contact whereby an electrical connection is made between said fixed contact and said resilient contact through the movable contact, the bimetallic element, and the spring conductor; and a reset button slidably supported on said base and arranged to engage said bimetallic element for resetting of the same.

3. A subassembly comprising a stud, a thermal snap-over element carried thereby, a spring element carried by the stud at one side of the thermal element and having one end shaped to limit snap-over of the thermal element and the other end shaped to make electrical contact, and a shield carried by the stud at the opposite side of the thermal element for at least partially protecting it from direct radiation from a heating element, the stud having a body portion located to the said one side of the thermal element, by which portion the mid region of the thermal element is adjustably positioned with respect to stops that are engageable with the ends or" the thermal element and are associated with the heating element, the spring construction of the spring element enabling the said other end thereof to continue to make electrical contact in spite of adjustment of the thermal element with respect to the aforesaid stops.

4. A subassembly as specified in claim 3, the said one end of the spring element taking the form of a flange extending toward one end of the thermal element for engagement therewith upon snap-over of the thermal element.

5. A subassembly as specified in claim 4, the shield contacting the thermal element onl at a mid region receiving the stud and being else" where spaced from the thermal element. v

6. A subassembly as specified in claim 3, the shield having a mid region receiving the stud in contact with the said mid region of the thermal element, the rest of the shield being displaced from the said mid region thereof so as to be spaced from the thermal element.

7. A thermal overload switch comprising an insulating base, a pair of terminals secured thereto, a heating element secured across the terwith the stops and movable away therefrom when heated by the heating element, and a stud having one end secured to a mid region of the thermal element and a body portion extending from said end into the insulating base on the side of the thermal element away from the heating element.

8. The thermal overload switch specified in claim 7 and further comprising a contact mounted on the insulating base, a shield secured to the stud between the thermal element and the heating element, the stud being adjustable in the insulating base to enable the mid region of the thermal element to occupy various positions with respect to the terminals, and a spring element secured to the stud at the side of the thermal element away from the heating element and the shield and engaging the contact at the said various positions of the thermal element, whereby electrical connection between the contact and one of the terminals is effected through the spring element, the thermal element and the stop on the said one terminal at the said various positions.

9. The thermal overload switch specified in claim 8, the contact being resilient and being engaged one end of the spring element, the other end of the spring element being shaped to limit the snapping movement of the thermal element.

10. The thermal overload switch specified in claim 9, the said other end of the spring element being shaped as a flange extending toward one end of the thermal element to engage the same to limit snapping movement, the switch further comprising means for acting against the other end of the thermal element to reset it against the stops.

HERBERT L. BRUMP.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,116,093 Carlson May 3, 1938 2,145,722 Hall Jan, 31, 1939 2,312,915 Kurtz Mar. 2, 1943 2,439,338 Fuge et al Apr. 6, 1948 2,508,464. McCullough May 23, 1950 

